John McCain has vowed to make big cuts in the US nuclear arsenal if elected president and called for Russia and China to join a global effort to tackle nuclear proliferation.

The Republican candidate called for the strengthening of existing non-proliferation deals and the negotiation of new ones, warning that the world faced no greater threat than the spread of nuclear weapons. "The cold war ended almost 20 years ago, and the time has come to take further measures to reduce dramatically the number of nuclear weapons in the world's arsenals," he said in a speech at the University of Denver.

The remarks revealed stark differences between Mr McCain and President George W. Bush on several important non-proliferation issues. Mr McCain has sought to distance himself from Mr Bush in public while relying on his help to mobilise Republican donors behind closed doors.

The Arizona senator said he would consider signing treaties long opposed by the Bush administration - including the Comprehensive Test Ban Treaty and a fresh arms reduction deal with Russia - and vowed to scrap plans to develop a controversial "bunker busting" nuclear weapon.

John McCain has vowed to make big cuts in the US nuclear arsenal if elected president and called for Russia and China to join a global effort to tackle nuclear proliferation.

The Republican candidate called for the strengthening of existing non-proliferation deals and the negotiation of new ones, warning that the world faced no greater threat than the spread of nuclear weapons. "The cold war ended almost 20 years ago, and the time has come to take further measures to reduce dramatically the number of nuclear weapons in the world's arsenals," he said in a speech at the University of Denver.

The remarks revealed stark differences between Mr McCain and President George W. Bush on several important non-proliferation issues. Mr McCain has sought to distance himself from Mr Bush in public while relying on his help to mobilise Republican donors behind closed doors.

The Arizona senator said he would consider signing treaties long opposed by the Bush administration - including the Comprehensive Test Ban Treaty and a fresh arms reduction deal with Russia - and vowed to scrap plans to develop a controversial "bunker busting" nuclear weapon.

The speech was part of Mr McCain's efforts to strike a more internationalist style of foreign policy than the unilateralist approach often associated with Mr Bush. "The United States cannot and will not stop the spread of nuclear weapons by unilateral action," he said, promising to return the US to its tradition of "innovative thinking, broad-minded internationalism and determined diplomacy".

His call for a deal with Russia to replace the Strategic Arms Reduction Treaty, which expires next year, together with proposals to eliminate tactical nuclear weapons from Europe, represented a break not only from Bush administration policy but also from the more hostile attitude Mr McCain had previously taken towards Russia.

Many of Mr McCain's proposals echoed positions of Republican pragmatists such as George Schultz and Henry Kissinger, both former secretaries of state, leading some analysts to conclude that foreign policy "realists" have gained the ascendancy over "neoconservatives" within the McCain camp. But the speech also included tough language towards North Korea, reflecting scepticism among McCain advisers about diplomatic efforts to halt Pyongyang's nuclear programme.